Stop doing a pointless Array conversion

## Summary

Just do one traversal to select a new row. This improves over the previous approach which did three traversals, adding code complexity and slowing things down.

## Details

The previous code was scanning the entire list to deselect, and *then* doing a conversion to Array, updating the Array, and converting back into a List.

This is a bad design for a couple reasons:

1. This update could happen in the initial list traversal! The program ends up doing a ton of extra work to convert to and from Arrays and the end result is that the program is slower *and* the code is more complex.

2. It requires a dependency on the Array.Extra package. No need to bring that in otherwise.

Author: evancz

elm-v0.18.0/src/Main.elm

@@ -1,7 +1,6 @@
 module Main exposing (..)
 
 import Array exposing (Array)
-import Array.Extra
 import Html exposing (Html, Attribute, program, div, a, h1, span, button, table, td, tr, text)
 import Html.Attributes exposing (id, class, classList, attribute, type_, href)
 import Html.Events exposing (onClick)
@@ -312,32 +311,22 @@ update msg model =
             )
 
         Select index ->
-            ( { model
-                | rows =
-                    model.rows
-                        |> List.map
-                            (\row ->
-                                if row.selected == True then
-                                    { row | selected = False }
-                                else
-                                    row
-                            )
-                        |> Array.fromList
-                        |> Array.Extra.update index
-                            (\row ->
-                                { row
-                                    | selected = True
-                                }
-                            )
-                        |> Array.toList
-              }
-            , Cmd.none
-            )
+            ( { model | rows = List.indexedMap (select index) model.rows }, Cmd.none )
 
         UpdateSeed seed ->
             ( { model | seed = Just seed }, Cmd.none )
 
 
+select : Int -> Int -> Row -> Row
+select targetIndex index ({ id, label, selected } as row) =
+    if index == targetIndex then
+        Row id label True
+    else if selected == True then
+        Row id label False
+    else
+        row
+
+
 type alias Model =
     { seed : Maybe Seed
     , rows : List Row